Action Launcher update brings customizable Pixel 2-style dock search
So, aside from the fact that you get to use the Pixel 2's dock search box, but you'll also be able to customize it with your favorite background color, shape, as well as shortcuts. You can find all these personalization options under Action Launcher's Quickbar editor.
Action Launcher 29.0 is available for free in the Google Play Store right now. It requires devices running Android 4.1 and up, but some feature will only work on much newer versions of the OS.
source: Action Launcher
Things that are NOT allowed: